The art has provided many ways for a direction finder (DF) to determine the direction to an RF source (Target), mainly by various wave analysis procedures.
Direction finding techniques can be categorized in groups, those which find the direction of the Target based on the received signal amplitude, based on the received signal phase, based on received signal timing, or those which are based on several of said attributes of the received signal.
One of the major challenges all direction-finding techniques face, in most situations, but mainly within a reflective environment, is to overcome the multipath reflections problem. Multipath reflections can cause false indications regarding the direction of the targeted RF source. Reflection of waves is expected from nearby objects, such as walls, or metallic objects. Waves transmitted from a Target may be scattered and reflected from nearby objects such as one or more walls, and arrive to the direction finder via many waves and from many directions. The reflected waves are weaker due to the following facts: (a) the reflected waves travel a longer path; (b) The reflected waves are scattered to many directions; and (c) the reflected waves from an object suffer from reflection losses. The reflected waves arrive at the DF later than the direct wave due to the longer path. These reflections are combined with the direct wave, distorting the amplitude, phase, and time of arrival of the signal. In prior art direction finding techniques that are based on measuring the signals amplitude, phase, or time of arrival, these multi-path reflections cause sever errors in the direction finding.
Amplitude-Based Direction Finding Techniques:
These direction finding techniques use one or more antennas. An example of a single antenna direction finding is a rotational directional antenna. The direction from which the received signal strength (RSS) or received signal strength indication (RSSI), or equivalent thereof is the highest, is the expected direction to the Target. Amplitude based directional finders that use several antennas measure the RSS/RSSI at each antenna and calculate from these amplitude differences the Angle of Arrival (AOA) of the signal. An example for an amplitude directional finder which uses several antennas is the monopulse system.
Additional techniques assess the distance to the Target, based on the signal strength, and by triangulating several measurements calculate the location or the direction to the Target.
Phase-Based Direction Finding Techniques:
These directional finders use two or more antennas and measure the phase difference of the arrival of a signal in plurality of antennas and calculate from these phase differences the AOA of the signal. This group includes, for example, interferometer direction finder, correlative interferometer direction finder, passed array systems, etc.
Time-based directional finder techniques: These directional finders are also known as TOA (Time of Arrival) type directional finders. They use two or more antennas and measure the time difference of the arrival of a signal to plurality of antennas and calculate from these differences the AOA of the signal. This group includes, for example short and long base TOA, DTOA (Differential Time of Arrival) etc.
Monopulse DF Techniques:
This technique is mainly used in ELINT (Electronic Intelligence) systems and radars, to find the direction from which a pulsed radar signal or echo is received. The signal is received in two or more directional antennas. The signals in the antennas, usually highly directional antennas, are added in phase to create a sum (E) signal, and added in opposite phase to create a Difference (A) signal, in one or two dimensions, azimuth, elevation or both. Based on the E and A signal strengths, the direction of the Target is determined.
All said prior art techniques rely on one or more properties of the received signal, require at the direction finder (DF) either plurality of receiving antennas and/or at least one receiving directional antenna, and also requires relatively complicated calculations and analysis, while they have no knowledge about the antenna array structure and layout, radiation patterns and orientation of their Targets. The inclusion of either a plurality of antennas or a directional antenna at a small size DF is cumbersome and complicated. Therefore, said techniques and the associated structures are generally not suitable for small size and relatively simple wireless personal devices, such as cellular phones, PDAs, digital cameras, smart watches, smart glasses, remote-control devices, etc.
Such devices are small in size, are provided in many cases with one or more simple antennas, that can be (but not limited to) omni-directional antennas, or very low gain directional antennas, and are relatively of low cost. Furthermore, in many cases such devices comprise of only one receiving channel for each antenna, and therefore are not suitable for using the abovementioned prior art techniques, unless significantly increasing their size, and or price.
U.S. Pat. Nos. 8,405,549 and 8,988,283 by same applicant and inventors provide direction finding techniques and devices that do not depend on attributes of the signal, such as amplitude, phase, or time of arrival, and that can substantially overcome reflections of the signal from nearby objects, such as walls. The DFs in both U.S. Pat. Nos. 8,405,549 and 8,988,283 utilize an array of two, three, or four receiving antennas (such as, but not limited to, omni-directional antennas) that together with a hybrid junction are combined to create various directional reception patterns. Several of such directional reception patterns are alternately created during several modes of reception, respectively. During each of said reception modes, an attenuator is used at the directional finder to intentionally attenuate in a controlled manner the received signal from the Target device until a point of loss of communication (such as handshake), and the respective attenuation for causing said loss of reception is recorded. The direction to the transmitting Target device is then calculated based on a relative comparison between the recorded attenuations and the respective reception patterns that have been used.
As noted, in both U.S. Pat. Nos. 8,405,549 and 8,988,283 the DF applies alternately two or more directional reception patterns at the DF in order to calculate the direction to the Target device (which in turn issues the transmitted signal). It has been found by the inventors that such a structure is vulnerable to errors due to signals that are “parasitically” received at the DF through components other than the antennas. For example, the signal may be partially “received” at the RF amplifier of the DF due to induction over the wires or other components of the device that are not the antennas. In order to overcome this problem, at least partially, the RF amplifier at the DF may be positioned within a masking enclosure. However, even when such an enclosure is used, this phenomenon cannot be entirely eliminated. Moreover, the use of such a masking enclosure is relatively cumbersome and expensive, and is not suitable to mobile devices having small volume.
In still another aspect, in devices where an array of antennas is used for receiving at the direction finder, the effectiveness of the operation is significantly influenced when the DF is not maintained horizontally during the process of the direction finding. It is highly desired to release the DF from this requirement.
It is therefore an object of the present invention to provide a method, device, and system for finding the direction to another device.
It is still another object of the present invention to provide said system method and device that do not depend on attributes of the signal such as its amplitude, phase, or time of arrival.
It is another object of the invention to provide said method, device, and system that utilizes only a single receiving antenna having any radiation pattern at the direction finder.
It is still another object of the invention to release the DF from the requirement of maintaining the device horizontally while performing direction finding.
It is still another object of the invention to provide said method, device, and system that require minimal and compact-size hardware, a structure which is particularly adapted for use in small-size mobile devices, such as smart-phones, smart-watches, Google® Glasses, digital cameras, remote controls, etc.
It is another object of the present invention to provide a method, device and system that are particularly applicable for operation within close locations, such as buildings, malls, theaters, etc.
It is another object of this invention to apply sensors or combinations of sensors for compensating for the orientation of the DF and Target devices at the time when the measurement is made.
It is still another object of the present invention to provide said system method and device that are simple in structure and reliable.
It is still another object of the present invention to provide said system method and device that are capable of determining a relative location between Target devices that are located within the communication range.
It is another object of the present invention to display to a user in a radar alike manner at least one Target device, wherein said display indicates the relative direction, distance, height, or any combination thereof relative to the DF.
It is still another object of the present invention to enable a user to select at least one Target and define it as a “landmark” or “mark”, that are in turn serve as additional reference to other Targets.
It is still another object of the present invention to use the DF for distributing data of any type, or performing various types of operations on selected Targets following said Targets direction, distance or height determination.
Other objects and advantages of the invention will become apparent as the description proceeds.